1. Field of the Invention
The present invention relates to a passive equalizer and, more particularly, to a passive equalizer with negative impedance to increase a gain.
2. Description of Related Art
Passive equalizers are widely used in a high-speed serial communication link such as a high definition multimedia interface (HDMI). FIGS. 1a and 1b show a schematic diagram of a communication system with a typical passive equalizer 11. The passive equalizer 11 can be implemented as required at a position close to the transmitting side 1, as shown in FIG. 1a, or the receiving side, as shown in FIG. 1b, for compensation. FIG. 2 is a circuit diagram of a typical passive equalizer, which is comprised of passive elements such as resistor R, inductor L and capacitor C. FIG. 3 is a graph of a frequency response of gains for a typical passive equalizer. As shown in FIG. 3, the passive equalizer at high frequency has a gain close to −0.5 dB in the vertical axis, and close to one at most. Accordingly, the high frequency gain is restrained, and the signal restoring capability is poor. In addition, the feature values of the passive elements in the typical passive equalizer cannot be easily adjusted, resulting in losing the flexibility on use.
Therefore, it is desirable to provide an improved passive equalizer to mitigate and/or obviate the aforementioned problems.